The present invention relates to an ultrasonic wave nebulizer which atomizes water or liquid with small power consumption.
Conventionally, an ultrasonic wave nebulizer for atomizing water to adjust room humidity has been known. In that atomizer, an ultrasonic wave vibrator which vibrates in thickness direction is mounted at a bottom of a water tank. FIG. 1A shows a prior atomizer in which a tank 102 which has an ultrasonic wave vibrator 103 at the bottom of the same contains water 101. When the piezoelectric vibrator 103 vibrates, water column 104 is generated on surface of water 101, and the water column 104 generates fine mist.
FIG. 1B shows the relations between water depth (H) and amount of generated mist (vertical axis). When the vibration frequency is 1.7 MHz, and the diameter of the vibrator is 20 mm, the maximum generation of mist is obtained when the water depth is from H=30 mm to H=40 mm.
However, the prior atomizer has the disadvantage that the size of the device is rather large, since the vibrator must be mounted at the bottom of the water tank with the depth of 30-40 mm.
Further, the prior atomizer has the disadvantage that the power consumption is rather large as shown in FIG. 1C in which the horizontal axis shows the power consumption, and the vertical axis shows the amount of the mist. The minimum power consumption W.sub.0 in a prior art is around 6 watts. Since an atomizer for converting 400 cc/hour of water to mist consumes about 40 watts, power consumption is too high to a battery operating atomizer or a portable atomizer.
Another prior atomizer is shown in JP UM second publication 38950/88 as shown in FIGS. 2A and 2B, in which the numeral 111 is a cone shaped horn having a resonator plate 112 on one end having the smaller diameter of the horn 111, and a piezoelectric vibrator 113 on the other end having the larger diameter of the horn 111. The numeral 114 is a capillary tube for supplying water on the resonator plate 112. The length of the horn 111 or the length between the plate 112 and the vibrator 113 is designed to be half wavelength. As the vibrator of the vibrator 113 is amplified according to the ratio of the area of the plate 112 and the area of the vibrator 113, the amplitude of the plate 112 is very large, and the water drop on the plate 112 is atomized.
However, the atomizer of FIG. 2 has the disadvantages that (1) water drop only close to the outlet of the tube 114 is atomized, and so, the essential operation area of the plate 112 is small, (2) as the vibration is mechanically amplified, the horn must be manufactured very precisely, and the trouble would happen due to the difference of the thermal expansion between the vibrator and the horn, and (3) the size of mist is rather large (for instance 20 .mu.m), as the operation frequency must be rather low (100-150 kHz for instance) because of the mechanical amplification. If the plate 112 is covered with a mesh in order to provide fine mist, the conversion efficiency from water to mist is decreased because of the presence of a mesh.